Semiconductor device and manufacturing method thereof

A semiconductor device comprising:

• a gate electrode over a substrate;
• a first gate insulating film over the gate electrode, the first gate insulating film comprising silicon nitride;
• a second gate insulating film over the first gate insulating film, the second gate insulating film comprising silicon and oxygen;
• an oxide semiconductor film including a microcrystal over the second gate insulating film;
• and
• a passivation film over the oxide semiconductor film,
• wherein the passivation film comprises silicon and oxygen, and
• wherein the oxide semiconductor film comprises indium and zinc,
• wherein the oxide semiconductor film includes a first region and a second region,
• wherein the first region has higher crystallinity than the second region, and
• wherein the second region is located over the first region.